Electrified Downhill bike

[Metallover]

When you are onroad a full suspension bike with a hubmotor is pretty dang smooth. When offroad... I guess it isn't so good. Larger tires and better suspension would help, but yesterday during my offroad adventure the vibrations from the bumps made my forearms hurt like no other. Ouch!

Here's the 2806 on 36v.

[zeropointbug]

Okay, thanks for the post, so I would guess on:

14s A123/45volts for a 45km/h or 28mph

15s A123/48volts for a 48km/h or 30mph

Pretty well 1mph/Volt for the 2806 on a 26" rim.

Here is where my pickle is, I would like to make it a 14s pack for the sake of charging, have it a split pack of 2x 7s packs on a dual pack charger, straight forward right. BUT, I would like to run 48V for the extra speed or range, but I don't like the idea of charging 3x 5s packs split charge.

Now unless someone here knows of a 15s A123 balance charger available, then sure 15s is the way, otherwise, it's 14s. I will not be using a BMS (waste of money IMO).

[Metallover]

You could charge a123s straigh off a power supply and the pack would stay balanced. Ebikes, especially with hub motors seeing around 20a max, and a large capacity pack capable of 100s of Amps, don't even make these cells sweat. Look around on ES and see what they say about the a123 cells.

I dont balance charge my turnigy pack, although I balance them every five runs orand; they are never off by much. I charge them in a 6s 6p configuration...

The only thing you really need is a lvc. Hobbycity has a few alarms, I love the voltage and temperature monitor. Check the balance ever couple weeks with a voltmeter and balance charge if needed, but with a123s you should be ok.

[zeropointbug]

Well traditionally I have never balanced charged my A123 packs (checked my A123 thread?), but those are small R/C packs, not much cost in them... this is a $550 battery (still cheap compared to lipos!), I am not sure if I want to risk it, you know?

Unless the tolerances are even better than M1's, then sure I might go for a PSU charge. I know I will at least put balance plugs on obviously just for checking cell voltages if I didn't use balance charger.

I asking cell_man what he thinks.

[zeropointbug]

Cost of these 15Ah A123 prismatics:
$2.50/Ah x 15Ah
= $37/cell
= $0.77/Wh

For a 48volt pack:
16s1p pack - 720Wh - 51.2V nominal/15Ah rated
$592 + shipping

Rough calculations: @40km/h (25mph) conservative calcs, hypothetically if you drove 30 miles a day, using 100% DOD.

30 miles range (w/o pedal assist)
2000+ minimum cycle life (to 80% OC) - 100% DOD
= 60,000 miles minimum life mileage
=$0.01/mile over minimum life expectancy
=+$0.002/mile of electrical power bill @ 9 cent/KWh (the rate I pay in SK, Canada)

Pretty dang cheap transportation if you ask me. At the discharge rates you see with an ebike, these batts should last alot more than 2000 cycles if the pack is built properly.

Metallover, what are the capacities your Turnigy packs now? How old are they?

[Metallover]

I am using six 6s 5ah packs for a total of 10ah 66.6v. My pack is 666wh and yours is 768wh.

4 of my packs are 22 cycles old and I got them in january, so 4 months now. The other two packs are a couple months older and have 5-6 more cycles on them making for around 30 cycles on them.

I figured that I need to ride about 4500 miles on my bike the pay for it's initial cost in gas.

Here's another guy's gas/money log that you might find interesting - http://spreadsheets.google.com/ccc?k...WN091VHc&hl=en

[zeropointbug]

Very interesting. Your guys gas is so cheap! (relatively) We pay over $1.10/L here which is pretty much $4/US gallon... I guess this ebike will pay for itself faster here then.

Really, we pay more for everything here, gas, food, cars, everything... liquor! 24 beer is $48 here.

[Metallover]

Yeah just checked the prices and a 24 pack of coors is $17.

Cost of living is lower here, but so are the wages... South Dakota has $16.53/hr average for full time work.

[zeropointbug]

#$% you!!! Although Coors =


I don't know the average full time wage, but our minimum wage here is ~$9/h IIRC.

[zeropointbug]

Well I did a speed test, on a flat hard packed gravel road I was able to hit 54km/h (33.5mph) on the MTB under my own stength, not bad. My brother can hit 50km/h (31mph) So when electric he definitely wants to be able to hit at least 45km/h, and with pedal assist, 50km/h I'm sure.

I think I am going to stick with a 14s pack, as that allows using a balance charger like the 720i I already have. He wants to sell me on a BMS, but I don't feel it's necessary at all. I might as well get a 8s pack for my lawn mower to save on shipping as I was going to get some of these for it sooner or later.

I can't believe how economical these cells are, they have the power, the A123 toughest we have come to expect, the cycle life, and best of all they are now energy dense as lipo. $0.75/Wh Is cheap as chips once you think how long they last.

[johnrobholmes]

Those cells are very good for the price. The only problem is a battery management system, but that is a problem for all larger packs.


Glad to see others getting into the "hobby". It is a lot of fun, and is quite cheap transportation.

[zeropointbug]

They are GREAT cells, I can't believe I never heard of them before. Each cell is 400 g, 48Wh , that makes them 120Wh/kg, decent.

Their new 10Ah cell that will be coming out this year they say will be ~140-150Wh/kg, apparently.

I will not be running a BMS for it, it will be balance charged and it will be in a hermetically sealed battery enclosure (at least that is the plan) made fom machined black poly block, with handle formed into one end for easy carry. I am not running BMS because I really don't think it's necessary, for these reasons:

-They are A123 cells..... come on
-Will be balance charged, so you will see any cell that would be out of wack
-Discharged typically 60% DOD

The guy I am buying from says they are rated 15 year life, and 7000+ cycles @ 80% DOD. Cheapest battery over it's life compared to any other battery by far, by far.

[BrianG]

On the topic of charging: A simple way to do it would be to use a transformer that, when rectified and filtered, has ~5v higher voltage than the max voltage of the pack you are using, set up a constant current charge circuit (pretty simple), and then use a comparator IC that shuts off the charger at 3.6v/cell. It won't have the CV charge phase, but from what people say, very little charge is done at that point anyway.

So, if you are running 14s packs, that's 50.4v. Add 5v (to account for current source dropout) for 55v. The Y23695 3 in the link above would be ideal; wire the primaries in parallel and the secondaries in parallel, use bridge rectification, around 0.5F capacitance (can use an inexpensive car audio cap). The 40v AC output would be around 56v once rectified and filtered, and would provide over 10A charge rate. Add the CC source and cutoff circuits and be done with it. Balancing, if desired, can be done using multiple balancers, just overlap a cell on each so they are in sync.

Of course, this doesn't have cell count protection, but since it will be used just for a single application, it's fine.

[zeropointbug]

That sounds like a good idea actually... although half the stuff you said went over my head (source current dropout? )

I checked out the transformer, 15lbs is quite heavy, but it's not moving anywhere, who cares I guess. IF this were to be used I might want to get the BMS then as I takes care of balancing while being charged. 10amp charge sounds really nice, as it will be charged on a 720i at about 9amps, each side, so you have to do that twice. Looking for a dual output charger that can charge 7 cell packs... why not a 710i DUO, Hyperion?


Also, for another idea for emergency charging, say you are away from your charger and don't want to use your own effort to bike back (far away), I was thinking a small charging circuit built into the battery case. I was thinking just a couple amps at the most with a built in AC socket with protective rubber plug with a PC AC cord somewhere on the bike stored away.

[BrianG]

By CC dropout, I mean: The CC source circuit will consist of a voltage regulator configured as a CC source, and it has ~1.5v dropout, coupled with the V drop on the current programming resistor of 1.25v. The extra voltage is just a little extra to prevent the pass transistors from saturating when the cells are close to 3.6v (which would reduce the current) and to account for any deviation in supply voltage. Transistors by themselves could be used as a CC source, but their values do change with temperature and current, so a V reg is a better idea for consistent operation.

And actually, I made an error on the previous post. That 15lb transformer would actually be good for closer to 20A. So, you could either use that at 20A, or use a smaller (and lighter/cheaper) transformer for 10A. But as you said, the "base station charger" will probably stay in one place so moving it around is irrelevant. And for a small 2A on-bike charger, a similar idea could easily be made under 5lbs that will do the same thing.

Sure, you can use a Duo or whatever, but unless your charging station is located where the bike is (my R/C stuff is in my basement and my bike would be in the garage), it will be a PITA to move the charger, PS, and assorted cables around. Not to mention the charger/PS setup will be substantially more expensive.